Despite the preference expressed by surgeons for arthroscopy, arthrography remains the method of choice for investigating lesions of the knee joint. In order to produce optimal contrast regularly, a standardised method for the examination must be used. Fifteen thousand pneumoarthrograms have been performed using the standard technique introduced by Möhlmann. The diagnosis of various lesions is discussed, with special reference to the problem of the medial posterior cornu. The results are analysed and the reliability of the method is evaluated.